NOCTURNAL MAGNETIC FIELD EXPOSURE: GENDER-SPECIFIC EFFECTS ON HEART RATE VARIABILITY AND SLEEP.

Graham, C.; Sastre, A.; Cook, M. R.; Gerkovich, M. M.

Midwest Res. Inst., 425 Volker Blvd., Kansas City, MO 64110, e-mail: cgraham@mriresearch.org (RR/C.G., A.S., M.R.C., M.M.G.)

The authors examined the effects of nocturnal 60-Hz magnetic field exposure on heart rate (HR), heart rate variability (HRV), and sleep. Forty-six healthy volunteers, 24 women, 40-60 yr old (mean 46 +/- 4.8 yr), participated in the study. All had normal sinus rhythms, regular sleep and dietary habits, did not work evenings or at night, and were not taking any medications that could alter normal cardiac functions or sleeping patterns. The subjects were asked to sleep in the magnetic field exposure test facility at Midwest Res. Inst. (MRI), Kansas City, MO from 23:00 to 07:00 hr for two 2-night sessions spaced over a week. In each session, half the subjects were randomly selected for exposure to a circularly polarized 60-Hz, 28.3-uT (283-mG) magnetic field, presented intermittently using 1-hr "on" and 1-hr "off" periods, on the first night, and then sham exposure the second night. The remaining subjects were sham-exposed/exposed in the reverse order. The first 2-night session examined the effect of the magnetic field on HR and HRV while the second session focused on sleeping patterns. Subjects were instructed to not consume alcohol 24 hr before a test session and to have no caffeine after 17:00 hr on the day of a session. During the first 2-night session, electrocardiographic (ECG) sensors were attached to skin sites on the right clavicle and the seventh intercostal space under the left axillary midline for recording HR and HRV data. The subjects got into bed in the exposure test room at 23:00 hr, lights were turned out, and the double blind/exposure control system was activated. The subjects remained in bed until morning and were monitored through the night by closed circuit TV, open audio intercom, and the physiological recording system. In the second 2-night session, the subjects were monitored with electroencephalographic (EEG)/electrooculographic (EOG) electrodes for polysomnographic analysis. Subjects slept overnight in a sound-attenuated and air-conditioned test room (a cube about 2.4 m on a side) that resembled a small bedroom. The magnetic field generation system (described by Doynov et al., Bioelectromagnetics 20:101-111, 1999; BENER Abstract No. 18695) was controlled by software operating in conjunction with the function/waveform generator. The field was produced by a Hewlett Packard (model 33120A) function/waveform generator, two Techron (model 7571) power amplifiers, and Merritt-type horizontal and vertical concentric coil system located out of sight behind the walls, ceiling, and floor of the exposure room. During the 1-hr field off periods, the coil systems were not energized. During the field on periods, the field cycled on and off at 15-sec intervals. On sham exposure nights, the subjects were exposed only to the ambient, background 60-Hz magnetic field, which did not exceed 0.2 uT. During the HR/HRV experiment, the ECG data were stored offline for later analysis. During the polysomnographic experiment, EEG and EOG data were analyzed to determine the following parameters: (1) total sleep time (TST), (2) wake time, (3) sleep onset latency, (4) number of arousals, (5) number of awakenings, (6) sleep efficiency, (7) rapid eye movement (REM) latency, (8) REM sleep time, (9) stage 1 sleep, (10) stage 2 sleep, and (11) slow wave sleep (SWS). REM sleep time, stage 1 and 2 sleep, and SWS sleep were expressed as a percentage of TST. The data were tested statistically by ANOVA. Mean HRs of both female and male volunteers decreased overnight, as expected, on the sham exposure nights (from 73.5 to 67.6 beats/min and 64.6 to 59.5 beats/min, respectively). Magnetic field exposure did not affect mean HR in either sex. Mean total power in the HRV frequency spectrum increased over the night during sham exposure, from 38.4 to 42.6 msec2 in males and from 38 to 41.9 msec2 for females. Mean total power was not significantly affected by magnetic field exposure in either gender. However, exposure to the magnetic field significantly reduced low-frequency power (0.04-0.15 Hz) in the HRV spectrum for males (p=0.04), but not for females. Magnetic field exposure disrupted the sleep pattern of female volunteers, as manifested by a significant decrease in percentage time spent in REM sleep (from 23.2 +/- 1.1 to 21.0 +/- 0.9%, p=0.03), and a strong trend for decreases in TST and sleep efficiency (p=0.06). Magnetic field exposure did not significantly affect the sleep pattern in males. Subjective reports of sleep disruption and feelings of tiredness and fatigue on awakening were also more common in females after magnetic field exposure than on sham exposure nights. Comparing these results with the outcome of their earlier studies with 18-35 yr old men (Sastre et al., Bioelectromagnetics 19:98-106, 1998; BENER Abstract No. 17171), the authors concluded that nocturnal magnetic field exposure causes gender-specific effects on HRV and sleep in older men and women. The gender-specific results also replicate results obtained in the authors' previous studies with younger men and women. (28 Refs). [Copyright 2001, Information Ventures, Inc.]

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